“In times of war and disaster, the ruthless among the deserters often turn to banditry to survive, establishing lairs and hideaways in out-of-the-way locations.”
When you reach the cave, go inside and head into the chamber in the southwestern corner of the delve. There’s a tiny oasis there and a hole in the roof of the cavern. You’ll find the skyshard among the foliage.
According to the loading screen snippet, the Tangle used to serve as a hideout for bandits and deserters in less-than-fortunate times. Thankfully, there’s none of that now, and there isn’t even an echo of evil-doers inside. However, there’s a fair amount of senche-lions and other beasts, so keep on your toes. There’s a handful of them in the same room as the shard, and you’ll have defeat them in order to grab it.